There is no doubt that in recent years concern
about nutrition and health in urban areas has been increasing.
Several important publications have appeared, such as that of
Schürch and Favre [1] and the URBIS newsletter. Two workshops
have been held in Great Britain [2; 3], and an article on this
subject appeared in the Food and Nutrition Bulletin [4].

Definition of the urban environment

The nutritional condition of a population and
the causes of problems depend on among other things the
environmental characteristics of the community. Therefore it is
necessary to distinguish precisely between rural, urban, and
metropolitan areas. Until now, what constitutes an urban area has
been defined structurally by the number of inhabitants living in
the conglomeration: communities with more than 20,000 inhabitants
have generally been called urban. However, there are many
conglomerations with more than 20,000 inhabitants that are just
large villages and should be designated rural. Therefore, the
urban area needs to be defined from a functional, not a
structural, point of view.

A rural society lives mainly from agriculture,
whereas urban society depends on a higher level of economic
diversification. This can have important consequences with
respect to nutrition. Whereas the nutritional status of a rural
community often suffers from seasonal climatic fluctuations
[5-7], particularly when there is a latent lack of food, that of
an urban population is less influenced by such changes [8]
because of its economic diversity. In the case of drought, for
example, urban populations are affected less be cause of their
differentiated possible sources of income; the income of the
rural population, which depends mainly on agricultural
production, is affected severely by lack of rainfall.

The appearance of the metropolis in this
century makes a further functional definition necessary to
distinguish it from urban areas. The metropolis is more complex,
not only from the economic but also from the cultural and
environmental points of view. This may influence the etiology of
health and nutritional problems in different ways.

The importance of family income

Several studies have shown that the nutritional
status of a population is determined by its economic situation.
In general, the poorer the population, the higher the prevalence
of malnutrition. This can be demonstrated by comparing the gross
domestic product of countries and the nutritional status of their
populations [9], and also the nutritional status of populations
classified by their wages within a country or a smaller area of a
country [10], or even within a city [11]. For this reason
international development agencies, such as the World Bank, use
nutritional indicators to assess the level of development
achieved.

Within urban communities such as shanty towns,
slums, and residential areas, however, the nutritional status of
children as stratified by family income may not necessarily show
significant differences [12]. This could be due to the smaller
economic differences in the communities, but there may be other
reasons for it. Figure 1 shows the growth retardation of
preschool children from different socio-geographic areas of Sao
Paulo classified by their families' income level [11]. It can be
seen that an increase in family income does not result in a
linear decrease in growth retardation. In very poor communities,
improvement in family income first leads to increased body
growth, but further economic improvement has very little
biological effect in pre-school children.

Furthermore, children in the slums and shanty
towns are shorter than those from families of the same income
group in the residential areas. These two facts suggest that,
besides family income, other factors such as environment (water
supply, sewerage facilities, health services, etc.) or even
cultural background could limit growth. It has been shown in
other studies that socio-cultural factors within a community such
as origin and education of parents, or environmental factors such
as sanitation facilities, can be of much more importance than the
economic conditions of households [12; 13].

The metropolis shows several characteristics of
a biological system, such as hierarchical organization of its
elements, cybernetic control of subsystems, structural and
temporary oscillations and instability, a partially open and
partially closed state, and self organization of the structure
and its function [14]. Although the metropolis is subject to a
process of breakneck development, it has a high level of inherent
stability due to a variety of complex interrelationships. Greater
diversity and complexity in a biological system provide a better
buffer against environmental disturbances. This is valid also for
a complex system such as a metropolis.

To take the analogy further, what the intake of
energy and nutrients is to a micro-organism, income is to the
community and the family. On the basis of a survey undertaken in
Rio de Janeiro, Brazil, between 1980 and 1983 (during an economic
recession), it has been hypothesized that a deterioration in the
family wage does not necessarily lead to a decrease in the
nutritional status of children [15]. Families try to buffer the
decrease in the wages by purchasing cheaper foodstuffs, reducing
waste, and pursuing diversified forms of employment.

These facts lead to the conclusion that an
increase in family income alone does not necessarily lead to an
automatic improvement in nutritional conditions.

A new pattern of feeding practice

It has been observed worldwide that
urbanization reduces the period of breast-feeding and causes
earlier weaning. However, studies in Sao Paulo and Rio de Janeiro
show a new trend. More and more mothers tend to breast-feed their
children longer [15; 16]. Those who are establishing this new
feeding pattern are better-educated mothers from higher-income
families.

New patterns of nutritional problems

Malnutrition

The inhabitants of metropolitan areas (and
their nutritional problems) are more heterogeneous than those of
rural areas. On the one hand we find a society living under poor
socio-economic conditions displaying the classic problems of
malnutrition. In epidemiological studies carried out between 1983
and 1986 in the three largest metropolitan areas of Brazil,
infants and pre-school children mainly showed a high prevalence
of stunting (10%15%), but a low prevalence of wasting (2%-5%)
[11; 12; 15]. The reduction in body growth rate and weight was
found only in children 10 to 12 months old and older (fig. 2). In
contrast to the case in rural areas, this growth retardation
started several months after breast-feeding had ceased and
dietary supplementation commenced [12]. These data may indicate
that malnutrition in this age group is caused less by hunger (or,
rather, lack of energy) than by poor sanitation and health
facilities.

School-age children show a different picture.
The older those from the deprived section of the population
become, the higher the prevalence of wasting, without there being
a major increase in stunting [17]. Children in some government
schools showed a prevalence of wasting of up to 24%.
Undernutrition seems to increase in this age group, although all
the schools surveyed maintained feeding programmes with food of
appropriate quality. There may be different causes (such as low
food intake in the family or in the school) that are as yet
unknown.

On the other hand, there is a
socio-economically better-off group which displays the
nutritional problems of populations of the industrialized
countries. For instance, children at a private school in the
above mentioned study area displayed a prevalence of obesity of
18% [17].

In the metropolitan areas of Brazil anaemia
seems to be more prevalent than acute malnutrition (tables 1 and
2). Two studies [12; 18] found no association between these
nutritional problems. This may indicate that in metropolitan
areas there are more groups with different nutritional risks.

Neglected urban risk groups

The paucity of data currently available
demonstrates that the comparison of social categories such as
urban and rural is too broad and non-specific to help us
understand the nutritional problems of the metropolitan
population, since urban society and the causes of nutritional
problems are too heterogeneous to allow generalizations. It seems
rather more useful to identify risk groups and search for the
causes of their particular problems.

In most cases, pregnant women, lactating
mothers, and infants are the main risk groups in rural
communities, and, therefore, nutritional surveillance and
interventions are concentrated on them. However, it is not clear
whether the pattern of risk is the same in urban areas. In
Brazil, there are some indications that deterioration of
nutritional status in low-income families due to food restriction
during economic crises occurs particularly in older children
(table 2) and physically highly active adults [19], and less in
infants [15].

The elderly

Until now, international nutritional research
has mainly been concerned with mothers and children as the most
vulnerable groups. The life expectancy of the population in
developing countries is increasing [9]. With the slow decrease in
birth rate, the proportion of elderly people in these societies
is growing. This is particularly so in urban regions, where life
expectancy is higher and the birth rate is lower than in rural
areas. We are far from knowing the magnitude and gravity of
nutritional problems of the elderly in developing countries.
There is not even a simple, widely accepted methodology for
measuring their nutritional status, such as exists for infants
and children (e.g., anthropometry).

The urban homeless

Despite the fact that homelessness is
recognized as a serious and growing urban problem, the magnitude
and causes of this problem are not known. Since the part of the
population that is homeless has no stable physical base, it is
difficult to evolve scientifically acceptable methods for
estimating their number and composition. Estimates of the number
of homeless in the United States vary from about 250,000 to
upwards of 3 million [20]. Practically no data are available from
urban areas of developing countries. Unaffiliated persons living
in extreme poverty suffer from an extremely high prevalence of
physical and mental disability.

Within the homeless population, street children
need special consideration. In contrast to the homeless adult,
who often lives in social isolation without permanent contact
with any other person, street children respond to the challenge
of their life problems by interacting with other children, from
informal groups to highly structured gangs.

The prevalence of malnutrition in these
children varies considerably, depending on the city [21]. In
Bogota, for example, vitamin deficiency and malnutrition seem not
to be serious problems because most restaurants allow street
children to scrape leftovers from the plates. In contrast, in
Karachi and Calcutta many of these children are malnourished. The
lack of hygiene, early sexual contacts and prostitution, the wide
use of drugs, and the inaccessibility of health care facilities
are responsible for high morbidity, which in turn is directly or
indirectly connected to the nutritional status of this marginal
group.

TABLE 1. Prevalence of malnutntion in
children of various age groups living in different types of
dwelling area in cites in Brazil

For a long time it has been observed that the
prevalence of psycho-social disorders, such as depression, is
higher in urban than in rural areas [22]. On the basis of a
theory that, with the social process of urbanization, community
relationships (gemeinschaftlich) are replaced by secondary
networks (gesellschaftlich)

[23], and with the support of the findings of
other researchers [e.g. 24], the conclusion has been drawn that
the higher-risk psycho-social disorders are caused by the greater
social isolation of the urban population [22]. It has been
reported that rural habitation appears to be a buffer against
major psycho-social disorders [25]. According to one study,
though, the traditional urban-rural dichotomy may be
inappropriate for socio-psychiatric research, since differences
were found to be concentrated in two minorities, namely,
unemployed men and unpartnered women [26]. All these findings,
however, were made in developed countries with Western-style
societies. Little is known about the magnitude or causes of
psycho-social disorders in the metropolises of developing
countries. If the observations of Kovness et al. [26] are also to
be found there, the magnitude of the problem is likely to be much
greater.

Individuals with psycho-social disorders often
show significant weight loss or gain due to poor or increased
appetite. However, we do not know to what extent the disorders
lead directly or indirectly to the various forms of malnutrition.
The whole syndrome, including loss of interest in activities and
lack of energy, diminished ability to concentrate,
indecisiveness, and decreased effectiveness and work
productivity, may lead to neglect of the rest of the family. This
culminates in poorer nutritional status of the most vulnerable
group, the children.

Infections

Because of the differences in ecology in
metropolitan dwelling areas, the higher population densities, and
differences in social behaviour, the metropolitan risk profile
for infectious diseases differs from that in rural areas. For
example, urban populations without sanitation facilities show
higher prevalence rates for diarrhoeal diseases than do those in
rural areas [27].

The prevalence of human immune virus (HIV)
infections in Africa varies significantly between rural and urban
populations [28]. In Rwanda, 1.3% of the rural population are
infected, compared with nearly 18% in the urban conglomerations.
Although it is unclear whether nutritional status influences
susceptibility to HIV infection or affects the development of
manifest acquired immunodeficiency syndrome (AIDS), the drastic
reduction of weight that occurs during the development of the
disease means that its prevalence must be considered in future,
at least in the context of interpreting anthropometry in
nutritional monitoring and surveillance.

Pollution

As shown by highly industrialized countries,
precipitate industrialization and development may burden the
environment with incalculable amounts of substances, many of them
synthetics. Lack of financial resources has forced many
developing countries to dispense with expensive measures for
reducing this contamination. The high concentration of industry
combined with a high population density creates a particular
public health problem for urban populations. Cities such as
Alexandria [29], Jakarta [30], Mexico City [31], Bombay [32], and
Seoul [33] suffer from high air pollution. Many of the people
exposed to this contamination, unlike those in more industrially
developed countries, also show signs of malnutrition.

TABLE 3. Rates of diarrhoea and acute
respiratory infections (ARI) in pre-school children from
different socioeconomic strata of Sao Paulo

There are only minor differences between
different socio-economic and socio-geographic groups in Sao Paulo
in the prevalence of acute respiratory infections [34], in
contrast to the case for diarrhoea [35] (table 3). This may be
due to the widespread air pollution in the city. Although there
are some physiological indications that the stress of pollution
may impair the immune system and increase the requirement for
some particular nutrients in individuals, we do not know the
extent of interplay among three epidemiological factors: stress
from pollution, infectious diseases, and nutritional status.

Nutritional interventions in formal
health care facilities

Significant variation occurs in the
effectiveness of nutritional intervention through formal health
care facilities in the metropolitan areas of Brazil. It is much
more difficult to improve nutritional status by feeding
programmes in the metropolitan areas because of the complex
origins of nutritional problems and risk groups. Therefore it is
not practicable merely to copy feeding programmes from the rural
areas. For instance, the free distribution of a cup of milk to
each child from low-income families (programa de leite) deals
with protein-energy malnutrition, which is of low magnitude, but
not with the more urgent problem of anaemia. Moreover, school
feeding programmes do not solve the problem of wasting in school
children.

Conclusions

Although we are only beginning to gain
experience in the field of public health nutrition, some
conclusions can already be drawn.

First, we need more basic epidemiological
knowledge concerning risk groups, their nutritional problems, and
their ecology in the metropolitan areas in the subtropics and
tropics. The causal complexities will force science to take a
holistic, interdisciplinary approach to research. It must be
stressed, however, that interdisciplinary research needs more and
better co-ordination than currently exists, as well as human and
financial resources.

Second, to date, interventions in urban areas
have been based on rural experience and not on the different
patterns of causation of urban nutritional problems and different
health facilities. Therefore, research into appropriate
intervention measures and strategies based on the results of
epidemiological experience needs to be carried out. We can
already conclude that the high interrelationship of causes of
malnutrition will make it necessary for both individuals and
public institutions to take responsibility for intervention.

Third, epidemiological results for either the
entire urban system at the macro level or for isolated socio
geographic sub-systems at the micro level cannot completely
describe the complex nutritional and health situation of the
metropolitan population. It is therefore necessary to study both
the whole system and the different sub-systems.

Finally, it should be stressed that the causes
of nutritional problems of urban populations have yet to be
studied in depth.